Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is associated to infections and it has been suggested that vaccination can trigger the disease.

However, little is known about the specific association between clinically manifest influenza/influenza vaccine and CFS/ME.

As part of a registry surveillance of adverse effects after mass vaccination in Norway during the 2009 influenza A (H1N1) pandemic, we had the opportunity to estimate and contrast the risk of CFS/ME after infection and vaccination.

METHODS:

Using the unique personal identification number assigned to everybody who is registered as resident in Norway, we followed the complete Norwegian population as of October 1, 2009, through national registries of vaccination, communicable diseases, primary health, and specialist health care until December 31, 2012.

Hazard ratios (HRs) of CFS/ME, as diagnosed in the specialist health care services (diagnostic code G93.3 in the International Classification of Diseases, Version 10), after influenza infection and/or vaccination were estimated using Cox proportional-hazards regression.

RESULTS:

The incidence rate of CFS/ME was 2.08 per 100,000 person-months at risk.

The adjusted HR of CFS/ME after pandemic vaccination was 0.97 (95% confidence interval [CI]: 0.91-1.04), while it was 2.04 (95% CI: 1.78-2.33) after being diagnosed with influenza infection during the peak pandemic period.

CONCLUSIONS:

Pandemic influenza A (H1N1) infection was associated with a more than two-fold increased risk of CFS/ME.

We found no indication of increased risk of CFS/ME after vaccination.

Our findings are consistent with a model whereby symptomatic infection, rather than antigenic stimulation may trigger CFS/ME.

Interesting! I had a really bad case of H3N2 that kept me in bed for 3 months. This was a long time ago but was right before I started having ME/CFS symptoms. It gets confusing though because I was also bitten by numerous ticks around the same time.

HAH. Yeah right. The key here is the "per 100,000 person-months," which I think means they counted how often CFS/ME onset within a month of influenza diagnosis or vaccine shot. It takes time for the muscular damage of vaccines to snowball and eventually lead to CFS/ME, usually much longer than 1 month, up to years.

Anyone able to find how how exactly they did gathered the data and did their calculations?

The key here is the "per 100,000 person-months," which I think means they counted how often CFS/ME onset within a month of influenza diagnosis or vaccine shot.

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It does not mean that.

They state that they followed the population for 39 months (1 Oct 2009 to 31 Dec 2012). During this period they found that the overall incidence of ME/CFS was approximately 2 cases per 100,000 person-months.

So this means, for example, if you tracked 1000 people for 100 months (= around 8 years), you would expect 2 people out of the 1000 on average to come down with ME/CFS during that time.

They state that they followed the population for 39 months (1 Oct 2009 to 31 Dec 2012). During this period they found that the overall incidence of ME/CFS was approximately 2 cases per 100,000 person-months.

So this means, for example, if you tracked 1000 people for 100 months (= around 8 years), you would expect 2 people out of the 1000 on average to come down with ME/CFS during that time.

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Yeah I know it means that. I was wondering why they did, because I'm trying to figure out how they did their analysis. It says "The adjusted HR of CFS/ME after pandemic vaccination was 0.97." "after pandemic vaccination" sounds like they used a time period, during/after a "pandemic." And how did they "adjust" it? Did they count the number of vaccines used? Basically, there are lots of ways their analysis could be faulty, but I have no idea what they might be if I don't know their exact methodology.

Never heard such a thing.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4246686/
That's one general mechanism behind it. Basically, they contribute to altering the mechanics of the shoulder joints. Over time other stress (sedentarism/injuries/other stuff) build on that alteration until one shoulder goes in one direction and the other shoulder goes in another, creating a wringing effect on the torso, neck, spine, skull, and down into the hips and below. Like twisting the water out of a towel... a metaphor.

These complete nation cohort studies are interesting and there should be more studies like this. The problem is that it only works for vaccinations that are not used by the large majority of the population. So the possibilities are the influenza vaccines and other vaccines when they are first adopted (eg the HPV vaccine).

The results show clear evidence of a post-infectious syndrome associated with influenza infections.

However a major limitation of this study is that in addition to confirmed laboratory testing of H1N1 in some subjects, they also assumed this in others:

We assume that the majority of subjects with influenza-like symptoms who received an R80 code in the period October–December 2009 were infected with the H1N1 influenza virus rather than another respiratory pathogen. No other influenza virus was known to be circulating in the population at this time.

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There was evidence of some people vaccinated who had an R80 code and this was similarly associated with a CFS diagnosis (HR:1.88 CI:1.46–2.42), compared to those who were not vaccinated, but had an infection.
It is arguable that some of these cases could be as a consequence of the vaccine, but these were a small minority of the overall number of cases (63 vs several thousand). With this data, it is impossible to tell between cases where the vaccine was simply ineffective vs cases where the vaccine might have triggered flu-like symptoms, and the patient received a diagnosis for an infection and later a CFS diagnosis.

The overall ME/CFS incidence rate is interesting and this is perhaps the most interesting part of this study. 2.08 per 100,000 person-months or 0.00025 person-years or 0.6% of the nation over 25 years. (this is an extrapolation and is not statistically valid).

But if flu is associated with increased risk then shouldn't it follow that vaccination should demonstrate lowered risk?

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That is a great question.

Unless influenza was the predomnant/most common trigger for this illness (study suggests the virus is a trigger for ~4% of cases), this study lacks the statistical power to demonstrate a reduction in risk. Side note: the hazard ratios were calculated using the Not infected/not vaccinated group as the baseline.

Here is the data, I hope this makes things a little clearer:

Magnus et al. said:

Table 3. Incidence rates and hazards ratios (HRs) of CFS/ME, with associated 95% confidence intervals (CIs), according to exposure to pandemic vaccination and influenza infection. Follow-up time from October 1, 2009, through December 31, 2012, for 4822,377 residents of Norway born 1899–2009.

So how does this two-fold plus increase in incidence post H1N1 stack up with a stochastic autoimmune mechanism. Perhaps the first reporting of symptoms associated with infection are the 'unmasking' of the pre-existing autoimmune process but any common infection should have the same effect? Unless H1N1 symptoms are particularly severe leading to increased or early reporting of ME/CFS onset?

An alternative explanation consistent with an autoimmune etiology may involve transient BBB permeability during severe infection?

Thanks Snow Leopard, I was just about to ask how they they knew that the patients had the flu. Do you mean that there was some confirmatory testing for H1N1 for those who subsequently developed ME?

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What I said before might be a little confusing. To clarify, there were two sources of data on infection.

Magnus et al. said:

Information on infection with the H1N1 influenza virus was obtained from two different sources. One source was from consultations in primary health care and emergency outpatient clinics, where all consultations must be reported to obtain reimbursement. Diagnoses are reported with codes from the International Classification of Primary Care, Second Edition (ICPC-2). The code for influenza-like illness (R80) was taken as a measure of H1N1 infection when the diagnosis was made during the pandemic peak period (October 1 through December 31, 2009). We considered R80 codes outside this period as insufficiently specific to be used as evidence for exposure to H1N1, as other infections may have caused similar symptoms. The other source of information on influenza infection was registrations in the Norwegian Surveillance System for Communicable Diseases of a confirmed antigenic test for H1N1 as reported from microbiology laboratories. The majority of these infections were reported during the peak period. However, due to the high specificity of these tests, reports from outside the peak period were included.